Core Ideas Grain relative yield increased with depth to claypan, while switchgrass relative yield was unaffected. Grain yield was twice as temporally variable as switchgrass yield. Grain crops generally were more profitable than switchgrass across depth to claypan. Switchgrass has the capacity to reduce yield variability caused by depth to claypan. Diminished topsoil thickness, or depth to claypan (DTC), is a major cause of yield and profit depression in corn (Zea mays L.) and to a lesser extent in soybean [Glycine max (L.) Merr.] production on claypan soils in the U.S. Midwest. Perennial grasses, such as switchgrass (Panicum virgatum L.), may be more resilient to reduced DTC than grain crops. Therefore, a study was conducted on a Missouri claypan soil to compare production and profitability of switchgrass grown for bioenergy to corn and soybean grain over varying DTC. Corn, soybean, and switchgrass yield were measured from 2009 to 2015 on plots constructed with DTC representative of those found on claypan landscapes. Yield, annual by‐crop relative yield (RY), yield coefficient of variation (CV), and return to land and management (net return) were evaluated by year, within wet and dry year categories, and across all years. Results indicate that corn and soybean RY across years increased to a maximum of 82 and 79% at DTC of 32 and 21 cm, respectively. Switchgrass RY was unresponsive and averaged 72% across DTC. Corn, soybean, and switchgrass yield CV averaged 46, 35, and 17%, respectively. Corn and switchgrass net return increased with DTC to a maximum of US$386 and $134 ha−1 at DTC of 31 and 32 cm, respectively, while soybean net return averaged $634 ha−1 across DTC. In general, switchgrass yield was less variable than grain production across DTC, and switchgrass could compete economically with corn on shallow DTC (<3 cm).

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Core Ideas Depth to claypan, landscape position, and cropping system influence soil fertility and nutrient buffering. Accounting for landscape‐variable depth to claypan could improve P and K management. Cover crops can help increase soil organic matter content. Cover crops may help reduce P requirements on claypan soils. Precise nutrient management across claypan soil landscapes requires an understanding of how diversity in management practices impacts soil properties and nutrient buffering. Therefore, a study was performed at the Central Mississippi River Basin site of the USDA Long‐Term Agroecosystem Network from 2010 to 2016 to determine how depth to claypan (DTC), cropping system (CS), and landscape position (LP) affect soil properties, and whether accounting for these factors could improve fertility management. Treatments consisted of five CS {MTCS, mulch till corn (Zea mays L.)–soybean [Glycine max (L.) Merr.]; NTCS, no‐till corn–soybean; NTCSW, no‐till corn–soybean–wheat (Triticum aestivum L.)–cover crop; CCRP, cool season conservation reserve program; and HAY, cool and warm‐season hay} and three LP (summit, backslope, and footslope), each with a distinct DTC. Soil test P (STP) was 9 kg P ha–1 greater on footslopes than summits. Soil test K (STK) and soil organic matter content (SOM) were greatest on backslopes and averaged 384 kg K ha–1 and 20 g kg–1, respectively, Soil test P was ≥49% and STK was ≥10% lower in NTCSW than in MTCS or NTCS. However, crop diversity in NTCSW maintained STP and increased SOM 2 g kg–1 over MTCS. Soil test P, pHs, and SOM were similar between CCRP and HAY, while STK in CCRP was greater at all LP. Lastly, deeper DTC caused greater P buffering and less K buffering than shallower DTC. These results indicate that eroded sideslopes with shallow DTC likely need more or more frequent P and less K than other LP.

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